Such an additive is known from WO 01/0719, in which antimony trioxide with a particle size of at least 0.5 μm is applied as the absorber. The additive is applied in polymeric compositions in such a content that the composition contains at least 0.1 wt. % of the additive so as to be able to apply a dark marking against a light background in the composition. Preferably a nacreous pigment is further added to obtain a better contrast.
The known additive has the disadvantage that in many cases, in particular in compositions with polymers that in themselves are only weakly carbonizing, only a poor contrast can be obtained by laser irradiation.
The aim of the invention is, to provide an additive that, also when mixed into polymers that in themselves are weakly carbonizing, produces a composition that is capable of being written with laser light with a good contrast.
This aim is achieved according to the invention in that the additive comprises particles that contain at least a first polymer with a first functional group and 0-95 wt. % of an absorber, the weight percentage being related to the total of the first polymer and the absorber and the first polymer being bound in at least a part of the surface of the particles by means of the first functional group to a second functional group, which is bound to a second polymer.
Upon irradiation with laser light polymeric compositions that contain the additive according to the invention area found to produce an unexpectedly high contrast between the irradiated and non-irradiated parts. This contrast is also significantly higher than when a composition is applied that contains only the absorber and the first or the second polymer.